The number of American households watching television broadcasts on the Internet has nearly doubled since 2006, according to a new report published by the market research firms The Conference Board and TNS. According to their analysis, nearly one-fifth of American households with Internet access now use it to watch TV—and 72 percent of online households access the Internet for entertainment purposes on a daily basis.

“Most consumers are pressed for time and require flexibility in their daily schedules and TV viewing habits,” said Lynn Franco, director of The Conference Board Consumer Research Center. “Being able to watch broadcasts on their own time and at their convenience are clearly reasons why we are seeing a greater number turning to the Internet. And it is the reason why we expect to see this trend continue.”

Citing an ongoing “shift from appointment TV to content on demand” and the firms report that 68 percent of the online TV viewers they surveyed were streaming video over the Internet. On the other hand, only 38 percent of respondents claimed to download free video content on a regular basis. The top two online-TV destinations were “official TV channel homepages” (65 percent of respondents watch programs on sites such as NBC.com and ABC.com) and YouTube.com (capturing a staggering 41 percent of viewers). Hmm, maybe Google wasn’t so crazy for spending $1.6 billion to acquire YouTube last year.

Other video sources included Apple’s iTunes.com, Hulu.com, social networking sites (e.g., FaceBook and MySpace), and the peer-to-peer file-sharing client Limewire. BitTorrent, curiously enough, wasn’t mentioned at all. The trend doesn’t look good for online movie-download services such as Vudu, either. The market-research firms report that “few consumers are willing to enroll in pay-per-download and subscription services.”